The present application relates to a secondary battery including an electrolyte layer containing an electrolytic solution and a polymer compound, and to a battery pack, an electric vehicle, an electric power storage system, an electric power tool, and an electronic apparatus that use the secondary battery.
In recent years, various electronic apparatuses such as a mobile phone and a personal digital assistant (PDA) have been widely used, and it has been demanded to further reduce the size and the weight of the electronic apparatuses and to achieve their long lives. Accordingly, as an electric power source for the electronic apparatuses, a battery, in particular, a small and light-weight secondary battery capable of providing high energy density has been developed.
In these days, it has been considered to apply such a secondary battery not only to the electronic apparatuses but also to other applications. Examples of such other applications may include a battery pack attachably and detachably mounted on the electronic apparatuses or the like, an electric vehicle such as an electric automobile, an electric power storage system such as a home electric power server, and an electric power tool such as an electric drill.
The secondary battery includes an electrolytic solution together with a cathode and an anode. The electrolytic solution is included in a secondary battery generally in a state that a separator is impregnated with the electrolytic solution. In addition thereto, in some cases, the electrolytic solution may be included in a secondary battery in a state of being supported by a polymer compound. In this case, the secondary battery includes an electrolyte layer as a so-called gel electrolyte. In such a secondary battery including the electrolyte layer, leakage of the electrolytic solution is prevented.
The configuration of the polymer compound contained in the electrolyte layer may largely affect battery characteristics of the secondary battery. Therefore, various studies have been made on the configuration of the polymer compound.
Specifically, in order to improve mobility of lithium ions, a random copolymer containing vinylidene fluoride and hexafluoro propylene as polymerization units or the like is used (for example, see U.S. Pat. No. 5,296,318). In order to improve energy density without damaging discharge load characteristics, a block copolymer containing vinylidene fluoride and hexafluoro propylene as polymerization units or the like is used (for example, see Japanese Unexamined Patent Application Publication No. 2000-123873). In order to prevent acute heat generation at the time of occurrence of internal short circuit or the like, as a denaturing agent, monomethyl maleate or the like is added to a random copolymer containing vinylidene fluoride and hexafluoro propylene as polymerization units or the like (for example, see Japanese Unexamined Patent Application Publication No. 2006-286496).